These circular flows have segments with two pieces: a larger backing piece and a smaller front piece. They are good to use in two specific instances:

A first message can be placed on the backing piece of the segment and then the front piece can be brought in through animation to convey a second message. Examples for this might be a old version of something being replaced by a new version, a question and then an answer, a wrong assumption replaced by a true assumption, etc.

Since the space between the segments is so small (to provide the most space for text message), sometimes adding a border line around a segment closes the space completely. Also sometimes the border line will have "spikes" when the angle is too sharp that look unnatural. The backing field can act as an outline instead of a border line, which maintains the space between segments so each segment is distinct.

Another reason to use them is their design appeal. Take a look at the tutorial for more usage and formatting tips.